Billions+ BC writers ⊕


Billions+BC Writers ⊕


Billions+ BC Writers
Gravity & Cooling

Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago.[24][25][26] Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.[n 5]

Earth's axis of rotation is tilted with respect to its orbital plane, producing seasons on Earth.[27] The gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, and gradually slows its rotation.[28] Earth is the densest planet in the Solar System and the largest of the four terrestrial planets.[29]

Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water, mostly by oceans.[30] The remaining 29% is land consisting of continentsand islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, and a convecting mantle that drives plate tectonics.

Within the first billion years of Earth's historylife appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms. Some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earth's distance from the Sun, physical properties, and geological history have allowed life to evolve and thrive.[31][32] In the history of the Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species[33] that ever lived on Earth are extinct.[34][35] Estimates of the number of species on Earth today vary widely;[36][37][38] most species have not been described.[39] Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival.[40] Humans have developed diverse societies and cultures; politically, the world has about 200 sovereign states.

Mineral Evolution

Mineral evolution is a theory that provides historical context to mineralogy. It postulates that mineralogy on planets and moons becomes increasingly complex as a result of changes in the physical, chemical and biological environment. In the Solar System, the number of mineral species has grown from about a dozen to over 5300 as a result of three processes: separation and concentration of elements; greater ranges of temperature and pressure coupled with the action of volatiles; and new chemical pathways provided by living organisms.

On Earth, there were three eras of mineral evolution. The birth of the Sun and formation of asteroids and planets increased the number of minerals to about 250. Repeated reworking of the crust and mantle through processes such as partial melting and plate tectonics increased the total to about 1500. The remaining minerals, more than 2/3 of the total, were the result of chemical changes mediated by living organisms, with the largest increase occurring after the Great Oxygenation Event.


After the formation of the Solar system, mineral evolution was driven by three primary mechanisms: the separation and concentration of elements; greater ranges of temperature and pressure combined with chemical action of volatiles; and new reaction pathways driven by living organisms.[9]

Separation and concentration

Cutaway views of some terrestrial planets, showing the layers.

The highest level in the classification of minerals is based on chemical composition.[10] However, the defining elements for many mineral groups, such as boron in borates and phosphorus in phosphates, were at first only present in concentrations of parts per million or less. This left little or no chance for them to come together and form minerals until external influences concentrated them.[11] Processes that separate and concentrate elements include planetary differentiation (for example, separation into layers such as a core and mantle); outgassingfractional crystallization; and partial melting.[1]

Intensive variables and volatiles

Gypsum crystals formed as the water evaporated in Lake LuceroNew Mexico.

Allowable combinations of elements in minerals are determined by thermodynamics; for an element to be added to a crystal at a given location, it must reduce the energy. At higher temperatures, many elements are interchangeable in minerals such as olivine.[3] As a planet cools, minerals became exposed to a greater range of intensive variables such as temperature and pressure,[1] allowing the formation of new phases and more specialized combinations of elements such as clay minerals and zeolites.[3] New minerals are formed when volatile compounds such as watercarbon dioxide and O2 react with them. Environments such as ice capsdry lakes, and exhumed metamorphic rock have distinctive suites of minerals.[1]

Biological influence

Life has made dramatic changes in the environment. Most dramatic was the Great Oxygenation Event, about 2.4 billion years ago, in which photosynthetic organisms flooded the atmosphere with oxygen. Living organisms also catalyze reactions, creating minerals such as aragonite that are not in equilibrium with their surroundings.[1][12]


Before the formation of the Solar System, there were about 12 minerals.[5] The estimate for the current number of minerals has been changing rapidly. In 2008, it was 4300,[1] but as of April 2018 there were 5312 officially recognized mineral species.[13]

Life on Earth

The evolutionary history of life on Earth traces the processes by which living and fossil organismsevolved, from the earliest emergence of life to the present. Earth formed about 4.5 billion years (Ga) ago and evidence suggests life emerged prior to 3.7 Ga.[1][2][3] (Although there is some evidence of life as early as 4.1 to 4.28 Ga, it remains controversial due to the possible non-biological fomation of the purported fossils.[1][4][5][6][7]) The similarities among all known present-day species indicate that they have diverged through the process of evolution from a common ancestor.[8] It is estimated that more than 99 percent of the roughly five billion species that ever lived on Earth are now extinct,[9] .[10][11]Estimates on the number of Earth's current species range from 10-14 million,[12][13] of which about 1.9 million have been named[14] and 1.6 million documented in a central database.[15] More recently, in May 2016, scientists estimated that 1 trillion species currently live on Earth, with only one-thousandth of a percent described.[16]

The earliest evidence of life comes from biogenic carbon signatures[2][3] and stromatolite fossils[17]discovered in 3.7 billion-year-old metasedimentary rocks from western Greenland. In 2015, possible "remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia.[18][19]In March 2017, putative evidence of possibly the oldest forms of life on Earth was reported in the form of fossilized microorganisms discovered in hydrothermal vent precipitates in the Nuvvuagittuq Belt of Quebec, Canada, that may have lived as early as 4.28 billion years ago, not long after the oceans formed 4.4 billion years ago, and not long after the formation of the Earth 4.54 billion years ago.[20][21]

Microbial mats of coexisting bacteria and archaea were the dominant form of life in the early Archean Epoch and many of the major steps in early evolution are thought to have taken place in this environment.[22] The evolution of photosynthesis, around 3.5 Ga, eventually led to a buildup of its waste product, oxygen, in the atmosphere, leading to the great oxygenation event, beginning around 2.4 Ga.[23] The earliest evidence of eukaryotes (complex cells with organelles) dates from 1.85 Ga,[24][25] and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. Later, around 1.7 Ga, multicellular organismsbegan to appear, with differentiated cells performing specialised functions.[26] Sexual reproduction, which involves the fusion of male and female reproductive cells (gametes) to create a zygote in a process called fertilization is, in contrast to asexual reproduction, the primary method of reproduction for the vast majority of macroscopic organisms, including almost all eukaryotes(which includes animals and plants).[27] However the origin and evolution of sexual reproductionremain a puzzle for biologists though it did evolve from a common ancestor that was a single celled eukaryotic species.[28] Bilateria, animals with a front and a back, appeared by 555 Ma (million years ago).[29]

The earliest complex land plants date back to around 850 Ma,[30] from carbon isotopes in Precambrian rocks, while algae-like multicellular land plants are dated back even to about 1 billion years ago,[31] although evidence suggests that microorganisms formed the earliest terrestrial ecosystems, at least 2.7 Ga.[32] Microorganisms are thought to have paved the way for the inception of land plants in the Ordovician. Land plants were so successful that they are thought to have contributed to the Late Devonian extinction event.[33] (The long causal chain implied seems to involve the success of early tree archaeopteris (1) drew down CO2 levels, leading to global cooling and lowered sea levels, (2) roots of archeopteris fostered soil development which increased rock weathering, and the subsequent nutrient run-off may have triggered algal blooms resulting in anoxic events which caused marine-life die-offs. Marine species were the primary victims of the Late Devonian extinction.)

Ediacara biota appear during the Ediacaran period,[34] while vertebrates, along with most other modern phyla originated about 525 Ma during the Cambrian explosion.[35] During the Permian period, synapsids, including the ancestors of mammals, dominated the land,[36] but most of this group became extinct in the Permian–Triassic extinction event 252 Ma.[37] During the recovery from this catastrophe, archosaurs became the most abundant land vertebrates;[38] one archosaur group, the dinosaurs, dominated the Jurassic and Cretaceous periods.[39] After the Cretaceous–Paleogene extinction event 66 Ma killed off the non-avian dinosaurs,[40] mammals increased rapidly in size and diversity.[41] Such mass extinctionsmay have accelerated evolution by providing opportunities for new groups of organisms to diversify.[42]